Printing apparatus, method of controlling printing apparatus, and storage medium

ABSTRACT

An embodiment of the present invention is a printing apparatus including: a print head including a plurality of nozzles each configured to eject a liquid droplet to a print medium; a control unit configured to control drive of each of the nozzles so as to eject the liquid droplet; a sensor configured to detect the liquid droplet ejected from each of the nozzles; a determination unit configured to perform determination as to whether or not stir of the liquid droplet is present in a case where each of the nozzles is driven by the control unit; and an adjustment unit configured to perform adjustment of an ejection interval between the nozzles in a case of detecting the liquid droplet by using the sensor, the adjustment being carried out based on the determination as to whether or not the stir is present.

BACKGROUND Field

The present disclosure relates to an ink jet printing apparatus, or morespecifically, to a technique for detecting a state of ejection of inkdroplets to be ejected from a print head.

Description of the Related Art

In an ink jet printing apparatus, it is important to understand a stateof ejection of ink droplets to be ejected from each of nozzles of aprint head in order to maintain constant quality of a printed image.Adaptation to higher image quality, higher speed, and diversification inloaded inks has been required in recent years. Moreover, reduction insize of ink droplets to be ejected from respective nozzles is inprogress. In particular, from the viewpoint of image formation, anejection speed and an amount of droplets of the ejected ink droplets areset to optimum values for each of ink colors in consideration of avariation among print heads or variations of physical properties amongthe ink colors. Nonetheless, it is known that a state of ejection of theejected ink droplets may change depending on a state of use of aprinting apparatus or environmental effects thereon. Variations inphysical properties of the ejected ink droplets (main droplets as wellas satellites being small droplets formed by fragmentation of the maindroplets) including ejection speeds (flying speeds), sizes, flyingintervals, ejection directions, and the like have also been ascertained.Accordingly, it is desirable to detect the state of ejection of theejected ink droplets before using the printing apparatus so as todetermine whether or not the ink droplets are successfully ejected orwhether or not the ejection speeds and other factors are normal even inthe case of the successful ejection.

In the course of detecting a state of ejection of liquid droplets suchas the ink droplets, there may be a case where the liquid droplets arestirred up due to a variation or turbulence of a surrounding airflow. Inthis case, detection accuracy is significantly deteriorated in the statewhere the stirred liquid droplets stay in the vicinity of a detectionelement. In this regard, even in the case where there are the stirredliquid droplets, it is still necessary to detect an ejection failurewhile suppressing an effect of the stir. Japanese Patent Laid-Open No.2004-42285 discloses a method of detecting an ejection failure to thisend.

Japanese Patent Laid-Open No. 2004-42285 discloses a method ofsuppressing an effect on liquid droplets that are stirred up due to avariation or turbulence of an airflow at the time of detection bysecuring predetermined suspension time after scanning with a carriage.This method does not require cumbersome operations or specialstructures, and is especially effective for suppressing the effect dueto the variation or turbulence of the airflow associated with the actionof the carriage.

SUMMARY

However, even under the situation where the effect of the airflowassociated with movement of the carriage is suppressed, a flyingdistance of each of ink droplets ejected from a head may be reduced andthe ink droplets may be stirred up without successfully reaching adetection area in a case where the ejection speed of the ink droplets islow. In the detection of an ejection failure adopting a configuration touse an optical sensor, ink droplets that are stirred up as a consequenceof a failure to reach the detection area will stay in the vicinity ofthe detection area in a case of using an ink having a low ejection speedor in a case where the ejection speed is reduced due to agingdegradation of nozzles. As a consequence, this configuration has aproblem of incapability of accurately determining an ejection failuredue to deterioration of detection accuracy.

In particular, the method according to Japanese Patent Laid-Open No.2004-42285 is based on the premise that the liquid droplets stably reachthe detection area. In this context, this method may fail to maintaindetection accuracy and erroneously determine an ejection failure in thecase of the low ejection speed of the liquid droplets.

Meanwhile, there is a method of carrying out a recovery action(so-called head cleaning) to resolve defective ejection of an ink byforcibly suctioning the ink in a nozzle from outside, and then carryingout an ejection failure detection operation again collectively as anoperation of an ink jet printing apparatus in a case of determination asbeing in a state of ejection failure. However, in a case of erroneousdetermination of the state of ejection failure due to the aforementionedeffect of the stir of the liquid droplets, this state does not changeeven after carrying out the recovery action and the unnecessary recoveryprocessing has to be repeated. Hence, a significant detection periodwill be required in this case.

Given the circumstances, an object of the present disclosure is tomaintain accuracy in detecting a state of ejection of liquid dropletsfrom a nozzle so as to prevent erroneous detection while suppressing anincrease in detection period.

An embodiment of the present invention is a printing apparatusincluding: a print head including a plurality of nozzles each configuredto eject a liquid droplet to a print medium; a control unit configuredto control drive of each of the nozzles so as to eject the liquiddroplet; a sensor configured to detect the liquid droplet ejected fromeach of the nozzles; a determination unit configured to performdetermination as to whether or not stir of the liquid droplet is presentin a case where each of the nozzles is driven by the control unit; andan adjustment unit configured to perform adjustment of an ejectioninterval between the nozzles in a case of detecting the liquid dropletby using the sensor, the adjustment being carried out based on thedetermination as to whether or not the stir is present.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing external appearance of a printing apparatus;

FIG. 2 is a perspective view showing an internal configuration of theprinting apparatus;

FIG. 3 is a block diagram showing a control configuration of theprinting apparatus;

FIGS. 4A and 4B are schematic diagrams for explaining a method ofdetecting a state of ejection of ink droplets;

FIGS. 5A and 5B are diagrams showing correlations between ejectionspeeds and flying distances of ink droplets;

FIGS. 6A and 6B are schematic diagrams showing a state of ejection in acase where ink droplets are stirred up;

FIG. 7 is a flowchart of processing to detect a state of ejection;

FIGS. 8A and 8B are graphs showing relations between positions ofejection and the number of detected nozzles;

FIG. 9 is a diagram showing locations targeted for re-inspection;

FIGS. 10A and 10B are diagrams for explaining a re-inspection method;and

FIG. 11 is a flowchart of processing to detect a state of ejection.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will be described below in detailwith reference to the accompanying drawings.

First Embodiment <General Outline of Printing Apparatus>

FIG. 1 is a diagram showing external appearance of an ink jet printingapparatus (hereinafter a printing apparatus) 100 representing an exampleof a liquid droplet ejection apparatus according to the presentembodiment.

The printing apparatus 100 includes a discharging guide 101 for stackingoutputted print media, operating buttons 102 used for setting printmodes, print paper, and the like, and a display panel 103 for displayinga variety of print information, setting results, and the like. Moreover,the printing apparatus 100 includes an ink tank unit 104 for containingink tanks to store color inks of black, cyan, magenta, yellow, and thelike and supplying the inks to a print head 201 (FIG. 2 ) representingan example of a liquid droplet ejecting head. The printing apparatus 100shown in FIG. 1 is a printing apparatus capable of printing on printmedia of several types with different widths up to 60-inch size printmedia. Rolled paper and cut paper can be used as the print media to beprinted with the printing apparatus 100. Note that the print media arenot limited only to the paper but may also be fabrics or vinyl, forexample.

FIG. 2 is a perspective view showing an internal configuration of theprinting apparatus 100. A platen 212 is a member which is located at aposition opposed to the print head 201 and is configured to support aprint medium 203 transported to this position. The print medium 203 istransported in a direction of transportation (y direction) by a sheettransport roller 213 while being supported by the platen 212. The printhead 201 is mounted on a carriage 202.

Moreover, the print head 201 includes a distance detection sensor 204for detecting a distance between the print medium 203 on the platen 212and the print head 201. The distance detection sensor 204 is an opticalsensor which is provided with a light emitting element to emit lightonto the print medium 203 and a light receiving element to receive thelight reflected from the print medium 203, and is configured to measurethe distance by using a change in output of an amount of light receivedby the light receiving element. A liquid droplet detection sensor 205 isan optical sensor configured to detect liquid droplets, which are inkdroplets in this case, to be ejected from the print head. The liquiddroplet detection sensor 205 includes a light emitting element 401(FIGS. 4A and 4B), a light receiving element 402 (FIGS. 4A and 4B), anda control circuit board 403 (FIGS. 4A and 4B). The liquid dropletdetection sensor 205 will be described later with reference to FIGS. 4Aand 4B.

A main rail 206 is designed to support the carriage 202. The carriage202 performs reciprocal scanning in x direction (an orthogonal directionto the direction of transportation of the print medium; hereinafterdefined as a main scanning direction) along the main rail 206. Thescanning with the carriage 202 is carried out by driving a carriagemotor 208 so as to move a carriage transportation belt 207. A linearscale 209 is arranged in a scanning direction in which the carriage 202performs scanning, and position information is obtained by causing anencoder sensor 210 mounted on the carriage 202 to detect the linearscale 209. In addition, the printing apparatus 100 includes a lift cam(not shown) for achieving stepwise displacement of a height of the mainrail 206 that supports the carriage 202, and a lift motor 211 fordriving the lift cam. A movement of the lift cam by driving the liftmotor 211 makes it possible to move the print head 201 up and down,thereby increasing and decreasing a distance between the print head 201and the print medium 203.

The print head 201 includes an ejection surface (so-called an orificeface) 201 a provided with ejection ports, and members for forming theejection ports as well as heaters that generate energy for ejectingliquids such as the inks are provided inside the ejection surface 201 a.The ejection surface 201 a is provided with common liquid chambers 214for the respective ink colors, so that the inks can be supplied toejection ports 216 arranged in rows through ink flow passages 215, andan image can be formed by ejecting the inks from the ejection portswhile using pressures generated by driving the heaters. A row ofejection ports for each ink color is formed by arranging the ejectionports 216 in the y direction. Such rows of ejection ports are arrangedin the x-axis direction. Moreover, each arranged row of ejection portsincludes 2048 nozzles. These nozzles are disposed in a staggered fashioninstead of a simple straight line. Accordingly, in a case where theejection ports on respective rows of nozzles are sequentially numberedfrom one end thereof, each row of nozzles is divided into two rows of anejection port row 217 including the ejection ports having odd numbersand an ejection port row 218 including the ejection ports having evennumbers. Here, the ejection port row including the ejection ports havingthe odd numbers will be referred to as an “odd number nozzle row” andthe ejection port row 218 including the ejection ports having the evennumbers will be referred to as an “even number nozzle row”. Accordingly,each of the odd number nozzle row and the even number nozzle row isformed from 1024 nozzles, and an interval between these nozzle rows isset to about 0.6 mm. Meanwhile, the odd number nozzle row and the evennumber nozzle row in each row of nozzles are combined together so as toachieve printing resolution of 1200 dpi (dots per inch), and a nozzlepitch in each of the odd number nozzle row and the even number nozzlerow is set to 600 dpi. In the meantime, a liquid droplet quantity ofeach ink droplet ejected from the ejection surface 201 a of the printhead 201 is set mainly in a range from about 4 pl to 6 pl.

FIG. 3 is a block diagram showing a control configuration of theprinting apparatus 100. The printing apparatus 100 includes a CPU 301that controls the entire apparatus, a sensor motor control unit 302 thatcontrols the respective sensors and the motor, and a memory 303 thatstores a variety of information including a state of ejection, athickness of a print medium, and so forth. The CPU 301, the sensor motorcontrol unit 302, and the memory 303 are connected to be communicablewith one another. The sensor motor control unit 302 controls thedistance detection sensor 204, the liquid droplet detection sensor 205,and the carriage motor 208 that causes the carriage 202 to performscanning. Moreover, the sensor motor control unit 302 controls a headcontrol circuit 305 based on the position information detected with theencoder sensor 210, thereby ejecting the inks from the print head 201.

Image data transmitted from a host apparatus 1 is converted intoejection signals by the CPU 301, and the print medium 203 is printed byejecting the inks from the print head 201 in accordance with theejection signals. The CPU 301 includes a driver unit 306, a sequencecontrol unit 307, an image processing unit 308, a timing control unit309, and a head control unit 310. The sequence control unit 307 performsoverall print control. To be more precise, the sequence control unit 307performs start and stop of the image processing unit 308, the timingcontrol unit 309, and the head control unit 310 serving as respectivefunctional blocks, transportation control of print media, scanningcontrol of the carriage 202, and the like. The control of the respectivefunctional blocks included in the CPU 301 is implemented by causing thesequence control unit 307 to read various programs out of the memory 303and to execute the programs. The driver unit 306 functions as an I/Ocontrol unit that controls input and output. For example, the driverunit 306 generates control signals for the sensor motor control unit302, the memory 303, the head control circuit 305, and the like based oninstructions from the sequence control unit 307, and transmits signalsinputted from the respective blocks to the sequence control unit 307.

The image processing unit 308 subjects the image data inputted from thehost apparatus 1 to color separation and converts data obtained by thecolor separation, thus performing image processing to convert theinputted image data into print data printable with the print head 201.The timing control unit 309 transfers the print data generated as aconsequence of conversion by the image processing unit 308 to the headcontrol unit 310 in conformity to a position of the carriage 202.Moreover, the timing control unit 309 also controls signals to besynchronized with ejection from the respective nozzles for determining astate of ejection of liquid droplets. The head control unit 310functions as a generation unit for generating the ejection signals, andis configured to convert the print data inputted from the timing controlunit 309 into the ejection signals and to output the ejection signals.Moreover, the head control unit 310 performs temperature control of theprint head 201 by outputting a control signal to the extent not to ejectthe inks based on an instruction from the sequence control unit 307. Thehead control circuit 305 functions as a generation unit for generatingdriving pulses, and is configured to generate the driving pulses inaccordance with the ejection signals inputted from the head control unit310 and to apply the driving pulses to the print head 201.

<Method of Detecting State of Ejection of Ink Droplets>

Next, a method of detecting a state of ejection of ink droplets to beejected from the print head 201 will be described with reference toFIGS. 4A and 4B. A diagram at an upper part of each of FIGS. 4A and 4Bshows a schematic diagram of the print head 201 and the liquid dropletdetection sensor 205 in the case of sectioning the printing apparatus100 along the y-z cross-section. As shown in FIGS. 4A and 4B, theejection ports (also referred to as nozzles) 216 for ejecting the inkdroplets of the respective ink colors are provided on the ejectionsurface 201 a of the print head 201 in order to generate images.

Meanwhile, a diagram at a lower part of each of FIGS. 4A and 4B shows atiming chart of an ejection signal for applying the driving pulses tothe print head 201 and a signal to be detected in a case where theliquid droplet detection sensor 205 detects passage of the ink dropletsejected from the ejection ports 216. As shown in FIGS. 4A and 4B, theprint head 201 includes the ejection surface 201 a. The liquid dropletdetection sensor 205 is formed from the light emitting element 401, thelight receiving element 402, the control circuit board 403, and thelike. The light emitting element 401 emits a light flux 404 and thelight receiving element 402 receives the light flux 404 emitted from thelight emitting element 401. The control circuit board 403 detects anamount of light received by the light receiving element 402. Acurrent-voltage conversion circuit configured to convert a currentflowing in accordance with the amount of light received by the lightreceiving element 402 into a voltage signal and to output the voltagesignal, and an amplification circuit for a level of a detection signalof the ink droplet are provided on the control circuit board 403. Inaddition, the control circuit board 403 is provided with provided with aclamping circuit for retaining a level of the signal to be outputtedfrom the amplification at a predetermined value (a clamping voltage)until a point immediately before observation of the ejection in order toeliminate effects such as saturation of the output and reduction in S/Nratio which are attributed to fluctuation of the level of the signal fordetecting ejection of the ink droplets due to an influence ofdisturbance. A very small variation factor as represented by ejection ofthe ink droplet is detected by using the above-mentioned circuits,whereby the level of the detection signal of ejection is secured at adesired level. As a consequence, the amount of light received by thelight receiving element 402 varies at the time of passage of each inkdroplet across the light flux 404 in the liquid droplet detection sensor205, and the state of ejection of the nozzles targeted for inspection isdetermined by using a result of comparison between the level of theoutputted detection signal and a predetermined reference voltage. In thepresent specification, a nozzle targeted for inspection will be definedas a “target nozzle” and a nozzle located in the vicinity of the targetnozzle will be defined as a “neighboring nozzle”.

Meanwhile, the liquid droplet detection sensor 205 is installed suchthat an optical axis of the light flux 404 is located at the sameposition in terms of z direction as a surface of the platen 212 on oneside that supports the print medium 203. Slits are provided in thevicinity of the light emitting element 401 and the light receivingelement 402, respectively, and the incident light flux 404 is narroweddown so as to improve the S/N ratio. A position in the x direction ofthe print head 201 to enable ejection of an ink droplet in such a waythat the ink droplet passes across the light flux 404 will be defined asa “detectable position”. In the case of detecting an ink droplet fordetecting the state of ejection of the ink droplet, the sensor motorcontrol unit 302 controls the carriage motor 208 in accordance with aninstruction from the sequence control unit 307, thereby moving the printhead 201 to the detectable position. A cross-sectional area of the lightflux 404 in the present embodiment is assumed to be about 2 mm×2 mm.Moreover, a parallel light projection area of the ink droplet in thecase where the ink droplet passes across the light flux 404 is assumedto be around 2{circumflex over ( )}−3 (mm{circumflex over ( )}2). Therow of ejection ports and the light flux 404 are arranged so as tosatisfy a relation of being parallel to each other, and a creepingdistance in a height direction (the z direction) therebetween is in setin a range from 2 to 20 mm. In the case where a creeping distancebetween each ejection port and the light flux 404 is reduced, it ispossible to detect the state of ejection stably because the light flux404 can detect the passage of the ink droplet at a closer positionrelative to a flying distance of the ejected ink droplet. However, inthe case where the row of ejection ports comes close to the light flux404, a diffused light component emitted from the light emitting element401 is reflected from the ejection surface 201 a of the print head 201,thereby generating a light quantity component to be received by thelight receiving element 402. As a consequence, this component mayoverlap the detection signal as a noise component in the course of thedetection of the state of ejection, and may therefore complicatefavorable detection. For this reason, regarding the creeping distancebetween the light flux 404 of the liquid droplet detection sensor 205and the row of ejection ports of the print head 201, it is desirable toconduct the detection of the state of ejection under a more preferablelayout in consideration of the above-described correlation. In themeantime, it is desirable to dispose the light flux 404 of the liquiddroplet detection sensor 205 and the platen 212 that supports the printmedium 203 substantially at the same height (the z direction) for thepurpose of harmonizing conditions in the case of detecting the state ofejection of the ink droplets by using the liquid droplet detectionsensor 205 with the state of ejection of the ink droplets to the printmedium 203 at the time of image formation.

Next, a configuration to detect the state ejection of the ink dropletsto be ejected and an ejection failure thereof will be described indetail. The diagram at the lower part of FIG. 4A is a graph showing aresult of detection by the liquid droplet detection sensor 205 in thecase where the ejection port 216 targeted for inspection (hereinafterreferred to as an “n-th nozzle”) of the state of ejection of the printhead 201 is successfully performing normal ejection, in theconfiguration as shown in the diagram at the upper part of FIG. 4A.Based on the ejection signal outputted from the head control unit 310and the head control circuit 305, the ink droplets are ejected towardthe liquid droplet detection sensor 205. The above-mentioned clampingcircuit is operated by a control signal synchronized with ejection ofthe ink droplets, and a signal level to be outputted is retained at apredetermined clamping voltage value immediately before observingejection of the ink droplets.

The operation by using the clamping circuit is cancelled immediatelybefore ejection of the ink droplets is started and the ink dropletsejected toward light flux 404 block the light. Moreover, a determinationis made as to whether or not the state of ejection is normal by using anamount of change in the case where the ink droplets block the light flux404. To be more precise, the normal state of ejection is determined bydetecting a fall (reference sign 406) below the reference voltage causedby a decline in light quantity that occurs at the time of passage of theejected ink droplets across the light flux 404 of the liquid dropletdetection sensor 205. Here, it is determined that the ink droplet isnormally ejected from the n-th nozzle targeted for inspection. Note thatFIG. 4A illustrates a result of ejection from the n-th nozzle targetedfor inspection more than once (a first shot and a second shot) in orderto obtain a more reliable result regarding the result of detection ofthe state of ejection by using the liquid droplet detection sensor 205.Regarding the state of each nozzle, the present disclosure defines astate where the nozzle can eject the ink normally as a “state of normalejection”, and defines a state where the nozzle fails to eject the inknormally due to clogging or the like as a “state of ejection failure”.

The diagram at the lower part of FIG. 4B is the graph showing a resultof detection in the case where the n-th nozzle targeted for inspection,which is subject to detection of the state of ejection of the print head201, fails to eject the ink droplets normally, as described above, asshown in the diagram at the upper part of FIG. 4B, or in other words, inthe case where the n-th nozzle is in the state of ejection failure. Aswith the case in FIG. 4A, the ink droplets are ejected toward the liquiddroplet detection sensor 205 based on the ejection signal outputted fromthe head control unit 310 and the head control circuit 305. However, theink droplets are not successfully ejected in the example of FIG. 4B, andthe ink droplets do not fly across the light flux 404. As a consequence,the ink droplets fail to block the light flux 404 and the expecteddecline in light quantity that would occur in the case where the normalejection takes place is not available (reference sign 407). Since thesignal output does not fall below the reference voltage, the n-th nozzletargeted for inspection is determined to be in the state of ejectionfailure where the ink droplets are not ejected normally.

Next, a description will be given of a problem at the time of detectionof the state of ejection failure in the above-described printingapparatus.

In the ink jet printing apparatus, the flying distance of the ejectedink is shortened in the case of the low ejection speed of the liquiddroplets ejected from the print head, and the ink may therefore fail toreach a detection area at a predetermined speed. In the ejection failureinspection with the configuration using the optical sensor, liquiddroplets that fail to reach the detection area and get stir up may stayin the air and block the light flux 404 in a case of using the inkhaving the low ejection speed or in the case where the ejection speed isreduced due to aging degradation of the nozzles. As a consequence, thereis a problem of incapability of accurate detection of an ejectionfailure due to deterioration of detection accuracy.

Next, a correlations between the ejection speeds and flying distances ofthe ink droplets (the liquid droplets) ejected from the respectiveejection ports 216 arrayed on the ejection surface 201 a of the printhead 201 will be described with reference to FIGS. 5A and 5B. In each ofgraphs shown in FIGS. 5A and 5B, the vertical axis indicates theejection speed of the ejected ink droplets and the horizontal axisindicates the flying distances of the ejected ink droplets. In a casewhere the gravitational force and the force of air resistance areapplied to the ink droplets ejected vertically downward from the printhead 201 is a stopped state, the ejection speed is gradually attenuatedand eventually reaches a constant speed, thus asymptotically convergingto a linear uniform motion. As a result of a test conducted by theinventor of the present application, in the case of an ink droplethaving an extremely small mass, the ejected ink droplet almost loses itsspeed down to 0 m/s at a moment of equilibrium between the gravitationalacceleration and air resistance, and eventually turns into a state offloating or staying in a weak airflow that flows around.

FIG. 5A shows behaviors of attenuation from initial speeds in a case ofejecting the ink droplet at an initial ejection speed of 20 m/s and in acase of ejecting the ink droplet at an initial ejection speed of 10 m/swhile setting a liquid droplet quantity of each ink droplet to 5.7 pl.As shown in FIG. 5A, in the case where the liquid droplet quantity isset to 5.7 pl, each ink droplet loses its velocity component andtransitions to a staying state in the case where the flying distance ofthe ejected ink droplet reaches a distance of about 17.4 mm or 10.7 mm.

On the other hand, FIG. 5B shows behaviors of attenuation from initialspeeds in a case of ejecting the ink droplet at an initial ejectionspeed of 20 m/s and in a case of ejecting the ink droplet at an initialejection speed of 10 m/s while setting the liquid droplet quantity ofeach ink droplet to 3.5 pl. As shown in FIG. 5B, in the case where theliquid droplet quantity is set to 3.5 pl, each ink droplet loses itsvelocity component and transitions to a staying state in the case wherethe flying distance of the ejected ink droplet reaches a distance ofabout 13.2 mm or 7.9 mm.

From the results shown in FIGS. 5A and 5B, it is understood that theflying distance of the ink droplet changes with the initial ejectionspeed at the time of ejection from the print head 201 regardless of theliquid droplet quantity of the ink droplet. It is also understood thatthe distance that the ink droplet can reach, or in other words, theflying distance of the ink droplet varies depending on the liquiddroplet quantity of the ejected ink droplet.

FIG. 6A is a schematic diagram showing a state where the ink dropletsejected from the nozzle are stirred up due to a drop in the ejectionspeed. As with the case in the diagram at the upper part of FIG. 4A, theink droplets are ejected toward the liquid droplet detection sensor 205based on the ejection signal outputted from the head control unit 310and the head control circuit 305. However, part of the ink dropletsejected do not reach the light flux 404 and stay in the upper part inFIG. 6A. As a consequence, the ink droplets fail to sufficiently blockthe light flux 404 and the expected decline in light quantity that wouldoccur in the case where the normal ejection takes place is notavailable. As a consequence, as shown in FIG. 6B, the signal output doesnot fall below a threshold voltage set equal to the value of thereference voltage, and the state of ejection cannot be detected. Here,the n-th nozzle targeted for inspection is detected to be in the stateof ejection failure even though this nozzle is achieving the normalejection. On the other hand, in the case where the ink droplets stay inthe light flux 404, the liquid droplet detection sensor 205 increasesthe current to be fed to the light emitting element 401 in order tomaintain the amount of light received by the light receiving element 402at a constant level. This leads to reduction in sensitivity to detectthe liquid droplets to be ejected subsequently, whereby accuracy isdegraded at the time of detecting the state of ejection of thesubsequent nozzle (an n+1-th nozzle) and so on.

Meanwhile, there is a method of carrying out a recovery action(so-called head cleaning) to resolve defective ejection of an ink byforcibly suctioning the ink in a nozzle from outside, and then carryingout an ejection failure detection operation again collectively as anoperation of an ink jet printing apparatus in a case of determination asbeing in a state of ejection failure. However, in a case of erroneousdetermination as the state of ejection failure due to an effect of stirof ink droplets, this state does not change even after carrying out therecovery action and the unnecessary recovery processing has to berepeated. Hence, a significant detection period will be required. Themethod according to Japanese Patent Laid-Open No. 2004-42285 is based onthe premise that the liquid droplets stably reach the detection area. Inthis context, this method may fail to maintain detection accuracy anderroneously determine an ejection failure in the case of the lowejection speed of the liquid droplets.

The present embodiment is designed to suppress degradation of detectionaccuracy due to the aforementioned effect of the stir of the liquiddroplets. Now, a detection operation of the state of ejection accordingto the present embodiment will be described below with reference to FIG.7 .

FIG. 7 is a flowchart of control according to the present embodimentconcerning processing to detect the state of ejection. The processing ofFIG. 7 is carried out at the time of an operation at initialinstallation in the case where a user operates the printing apparatus100 for the first time, or in a case where the user replaces the printhead 201 with a new one, or more specifically, immediately afterattachment of the new print head 201, and so forth. This processing mayalso be executed regularly by the user as maintenance work after usingthe printing apparatus 100 for a predetermined period. Moreover, theprocessing may be directly executed in accordance with an instruction bythe user. Note that the processing of FIG. 7 is the processing to becarried out by the sequence control unit 307 of the CPU 301 inaccordance with a program stored in the memory 303, for example.

In the case where the carriage 202 moves in the x direction shown inFIG. 2 and reaches in the vicinity of a preliminary ejection port wherethe preliminary ejection takes place, this movement of the carriagegenerates an airflow in a detection area for the liquid dropletdetection sensor 205 inside the preliminary ejection port. Accordingly,in the case where the detection operation of the state of ejectionassociated with the preliminary ejection is carried out immediatelyafter the print head 201 reaches an upper part of the preliminaryejection port, the airflow in the detection area is not stabilized andthe detection takes place in a state where ink droplets are apt to bestirred up as shown in FIGS. 5A and 5B. As a consequence, noise isincreased during the detection. For this reason, it is desirable tostart the detection operation of the state of ejection at preset timingsuch as a point in the course of a printing operation as well as beforeand after the printing operation based on image data (or print data)received by the printing apparatus, and a point of execution of asuctioning recovery action.

In step S701, the sequence control unit 307 moves the print head 201 202such that the encoder sensor 210 is located above the detection area(more specifically, above the upper part of the preliminary ejectionport that carries out the preliminary ejection). Note that theexpression “step SXXX” will be hereinafter abbreviated to “SXXX”.

In S702, the sequence control unit 307 stops the carriage 202 for apredetermined period. In this instance, neither the operation to movethe carriage 202 nor the ejection operation is carried out. Here, theperiod to stop the carriage 202 is set longer than a period required tosettle turbulence of the air in the detection area caused by themovement of the carriage 202. The stop period may vary depending on theshape of the preliminary ejection port, the shape and a moving speed ofthe carriage 202, a location of the liquid droplet detection sensor 205,and so forth. Although it is difficult to generally determine the stopperiod, the stop period is roughly a period in a range from several toseveral tens of seconds.

In S703, the sequence control unit 307 executes preliminary ejectionprocessing in order to inspect whether the nozzle is in the state ofnormal ejection or state of ejection failure.

In S704, the sequence control unit 307 detects the state of ejection ofthe nozzle by using the liquid droplet detection sensor 205. To be moreprecise, the light receiving element 402 can obtain a signal indicatingwhether or not the ink droplet ejected from the nozzle in S703 passesacross the light flux 404 by means of reception of the light. Thedetection processing in this step is executed one by one for all thenozzles provided to the print head 201. Moreover, a nozzle assessed tobe in the state of ejection failure in this step is determined to havean assumed ejection failure.

In S705, the sequence control unit 307 determines whether or not theinspection processing from S701 to S704 has been completed for all theprint heads provided to the printing apparatus. The processing proceedsto S706 in the case where a result of determination in this step istrue. On the other hand, in the case where the result of determinationin this step is false, the processing returns to S701 and the processingto detect the state of ejection of the next print head is executed.

In S706, the sequence control unit 307 determines the presence of anyabnormal nozzles in the print head 201 based on the result of theprocessing in S701 to S705. Here, an abnormal nozzle is the nozzle inthe state of ejection failure, or more specifically, the nozzledetermined to have the assumed ejection failure in S704. The processingproceeds to S707 in the case where an abnormal nozzle is determined tobe present in this step. On the other hand, the series of inspectionprocessing is terminated in the case of determination that there are noabnormal nozzles in this step.

In S707, the sequence control unit 307 carries out inspectionalpreliminary ejection processing for determining the presence of stir ofliquid droplets. To be more precise, a nozzle group including the nozzledetermined to have the assumed ejection failure in S704 and at least twonozzles located at anteroposterior positions relative to the formernozzle in the row of nozzles to which the former nozzle belongs isdesignated as a nozzle group including the nozzle determined to have theassumed ejection failure. Then, the designated nozzle group is subjectedto the preliminary ejection. Here, the number of nozzles included in thedesignated nozzle group, the number of ejected shots in the inspectionalpreliminary ejection are determined based on the specifications of theprinting apparatus targeted for inspection. For example, the nozzlegroup may consist of three nozzles in total including the nozzledetermined to have the assumed ejection failure and two nozzles locatedat the anteroposterior positions relative to the former nozzle (in otherwords, the nozzles adjacent to the nozzle determined to have the assumedejection failure in the y direction). Alternatively, the nozzle groupmay include two or more nozzles each at the anterior position and theposterior position as illustrated in FIG. 9 . After all, the number ofnozzles is preferably set to an appropriate number that can clearlybring about a difference between the number of liquid droplets detectedin the detection area and the number of liquid droplets detected in anon-detection area. In the meantime, an ejection method in thepreliminary ejection is carried out for each of the nozzles in thenozzle group determined in accordance with the above-mentioned method.Then, the carriage is moved in the x direction (the main scanningdirection) shown in FIG. 2 , and the ejection is carried out whilechanging the positions of ejection. Note that each of the terms“detection area” and “non-detection area” stated herein is assumed torepresent a predetermined partial area on xy plane of a nozzle orificesurface.

A start position and an end position (which are positions in the xdirection) of ejection in the inspectional preliminary ejectionprocessing in S707 are determined based on the specifications of theprinting apparatus targeted for inspection. In this instance, a homeside (a side where the print head is located during standby) may be setto the start position of ejection while an away side may be set to theend position thereof. Alternatively, the away side may be set to thestart position while the home side may be set to the end position. Inany case, the setting should be made in such a way as to include atleast an area where the ink droplets ejected from the nozzles of thenozzle group pass across the light flux and an area where the inkdroplets do not pass across the light flux. The respective nozzles inthe nozzle group are sequentially subjected to ejection of the ink. Inthe case where ejection from all of the nozzles in the nozzle group iscompleted, the carriage is moved to the next inspection position (aposition in the x direction) and then the similar operation is carriedout again. Here, a moving distance of the carriage is set to such adistance that is defined as a minimum moving distance in accordance withthe position information to be detected by using the linear scale 209arranged in the main scanning direction and the encoder sensor 210mounted on the carriage 202. The above-described operation is repeatedlycarried out until reaching the end position of ejection, and theinspection in S707 is terminated after completion of ejection at all ofthe inspection positions.

In S708, the sequence control unit 307 refers to a result of inspectionin S707, thereby determining the presence of the stir of the liquiddroplets. In the present embodiment, graphs showing the state ofejection of the liquid droplets as plotted in FIGS. 8A and 8B are usedin a method of determining the presence of the liquid droplets. In eachof the graphs shown in FIGS. 8A and 8B, the horizontal axis indicates anoutputted value from the encoder sensor 210 and the vertical axisindicates a counted value of the number of nozzles from which theejected liquid droplets are detected by the liquid droplet detectionsensor 205. The outputted value from the encoder sensor 210 representsthe position of the carriage in the main scanning direction.Accordingly, the outputted value schematically indicates the position inthe main scanning direction of the nozzle that performs the inspectionalpreliminary ejection. Meanwhile, in each of the graphs shown in FIGS. 8Aand 8B, each dotted line represents an end portion of the detectionarea. A graph 801 a in FIG. 8A is a graph showing a state in which eachnozzle is performing normal ejection without stirring up the liquiddroplets. On the other hand, a graph 801 b in FIG. 8B is a graph showinga state in which liquid droplets are stirred up.

In the case where no liquid droplets are stirred up, as shown in FIG.8A, almost all the nozzles that eject the liquid droplets are detectedin the detection area whereas no nozzles that eject the liquid dropletsare detected outside the detection area.

On the other hand, in the case where the liquid droplets are stirred up,as shown in FIG. 8B, disturbance in sensitivity is observed outside thedetection area more frequently than the normal case shown in FIG. 8A,and erroneous detection is prominent outside the detection area inparticular. In S708, reference is made to the graph plotted based on theresult of S707, and the case where there is disturbance in sensitivityoutside the detection area is determined as a state under an effect ofthe stir of the liquid droplets. Then, the processing proceeds to S709.On the other hand, in the case where no disturbance in sensitivity isobserved outside the detection area, this state is determined as a statewithout an effect of the stir of the liquid droplets. Then, theprocessing proceeds to S711. Here, as a means of determining thepresence of disturbance in sensitivity, an appropriate threshold may beset up in conformity to the specifications of the printing apparatus.Alternatively, a graph representing a result of ejection under similarejection conditions conducted before shipment of a product may be storedin advance in the memory 303 as a benchmark for indicating a normalstate of ejection, and this graph may be compared with the resultobtained in S707.

In S709, the sequence control unit 307 sets the row of nozzles (see FIG.9 ), which includes the nozzle group that is determined to be under theeffect of the stir of the liquid droplets, as a target for re-inspectionand then carries out the inspection processing again for detecting thestate of ejection. In the case of carrying out the re-inspection, theprocessing to detect the state of ejection is executed after adjustingan ejection interval (wait time) between the nozzles in order to preventthe disturbance in sensitivity attributed to the effect of the stir ofthe liquid droplets. Here, time that is longer than time with which itis possible to settle the stirred liquid droplets so that the majorityof the liquid droplets ejected in the preliminary ejection can reach awaste ink absorber 405 is set as the wait time (defined as t3; see FIGS.10A and 10B). This setting enables ejection of the next nozzle in thestate where the stirred liquid droplets generated by ejection aresettled. Accordingly, it is possible to accurately determine whether ornot the nozzle that is determined to have the assumed ejection failureis in the state of ejection failure. In the meantime, the wait time fora nozzle determined to have the stir of the liquid droplets is longerthan the wat time for a nozzle determined not to have the stir of theliquid droplets. The processing proceeds to S710 in the case wheredetection of the state of ejection of the nozzles included in all thenozzle groups targeted for re-inspection is completed. Here, the row ofnozzles including the nozzle group determined to be under the effect ofthe stir of the liquid droplets is targeted for re-inspection. Instead,only the relevant nozzle group may be targeted for re-inspection.

In S710, the sequence control unit 307 receives results in S707 to S709and determines the presence of an abnormal nozzle in the print head 201.The abnormal nozzle is a nozzle in the state of ejection failure. Theprocessing proceeds to S711 in the case where the abnormal nozzle isdetermined to be present in this step. On the other hand, the series ofprocessing is terminated in the case where no abnormal nozzles aredetermined to be present in this step.

In S711, the sequence control unit 307 determines whether or not thenumber of times of determination that the abnormal nozzle is presentreaches a given threshold (defined as n). Note that the threshold n usedin this step is assumed to be predetermined based on the use of theprinting apparatus targeted for inspection. In the case where the numberof times of determination that the abnormal nozzle is present reachesthe given threshold n and a result of determination in this step istrue, the series of the inspection processing shown in FIG. 7 isterminated and error processing will be carried out. Here, the errorprocessing is processing to display an error message and an error codeon the display panel 103 in order to notify the user of the presence ofa number of nozzles in the state of ejection failure. For example, in acase where the error message to be displayed intends to recommend apowerful cleaning operation, the user can resolve the state of ejectionfailure of the nozzles by operating a cleaning action which is morepowerful than head cleaning to be carried out in S712. On the otherhand, in a case where the error message notifies of a failure of a unitor recommends replacement thereof, the user can order repair service byconsulting with a manufacturer of the printing apparatus depending onthe condition of the failure of the printing apparatus. The processingproceeds to S712 in the case where the number of times of determinationthat the abnormal nozzle is present does not reach the given threshold nyet and the result of determination in this step is false.

In S712, the sequence control unit 307 executes the head cleaning as therecovery action for resolving the ejection failure of the nozzles.Thereafter, the processing returns to S701 and the processing to detectthe state of ejection of each nozzle is executed again.

Effect of Present Embodiment

According to the present embodiment, in a case where an arbitrary nozzleis subjected to inspection as to whether the nozzle is in the state ofnormal ejection or in the state of ejection failure, it is possible toavoid a case of erroneously detecting the nozzle as being in the stateof ejection failure due to an effect of stir of liquid droplets.Moreover, it is possible to reduce inspection time by avoiding executionof unnecessary recovery actions (head cleaning).

Second Embodiment

A second embodiment will be described below. In the followingdescription, different features from those in the first embodiment willmainly be discussed and explanations concerning the same details asthose in the first embodiment will be omitted as appropriate.

FIG. 11 is a flowchart of control according to the present embodimentconcerning processing to detect a state of ejection. The processing ofFIG. 11 is the processing to be carried out by the sequence control unit307 of the CPU 301 in accordance with a program stored in the memory303, for example. Of the processing shown in FIG. 11 , respectiveprocedures from S1106 to S1110 and from S1112 to S1113 are the same asthe respective procedures from S701 to S705 and from S711 to S712 inFIG. 7 . Accordingly, explanations concerning these overlapping portionswill be omitted.

The first embodiment is configured to carry out the inspection of thestir of the liquid droplets after the determination of the assumedejection failure in accordance with the ordinary detection of the stateof ejection (S707 to S705, . . . , S707 in FIG. 7 ). However, thisconfiguration may erroneously determine a nozzle in the state ofdetection failure as a nozzle in the state of normal ejection because ofthe liquid droplets that stay on the light flux depending on the timingto detect the state of ejection. Given the circumstances, according tothe present embodiment, all the nozzles are subjected to an inspectionconcerning the stir of the liquid droplets before carrying out thedetection of the state of ejection in order to improve detectionaccuracy.

In step S1101, the sequence control unit 307 moves the print head 201such that the encoder sensor 210 is located above the detection area.

In S1102, the sequence control unit 307 stops the carriage 202 for apredetermined period.

After the movement of the carriage is completed in S1101 and S1102, thesequence control unit 307 carries out the inspection for determining thepresence of stir of liquid droplets in S1103. In the present embodiment,all the nozzles provided to the print head 201 are subjected to thisinspectional preliminary ejection. Here, as with the first embodiment,the number of ejected shots in the inspectional preliminary ejection isdetermined based on the specifications of the printing apparatustargeted for inspection. Meanwhile, as for the ejection method in thepreliminary ejection, ejection is carried out while changing positionsin the x direction (see FIG. 2 ) for each row of nozzles.

In S1104, the sequence control unit 307 refers to a result of inspectionin S1103, thereby determining the presence of the stir of the liquiddroplets. As with the first embodiment, the graphs showing the state ofejection of the liquid droplets as plotted in FIGS. 8A and 8B are usedin the determination method in this step, and the determination iscarried out for each of the rows of nozzles. In S1104, reference is madeto a graph plotted based on the result of S1103. In the case where thereis disturbance in sensitivity outside the detection area, this state isdetermined as a state under the effect of the stir of the liquiddroplets. Then, the processing proceeds to S1105. On the other hand, inthe case where no disturbance in sensitivity is observed outside thedetection area, this state is determined as a state without an effect ofthe stir of the liquid droplets. Then, the processing proceeds to S1106.Here, as a means of determining the presence of disturbance insensitivity, an appropriate threshold may be set up in conformity to thespecifications of the printing apparatus as with the first embodiment.Alternatively, a graph representing a result of ejection under similarejection conditions conducted before shipment of a product may be storedin advance in the memory 303 as a benchmark, and this graph may becompared with the result obtained in S1103.

In S1105, the sequence control unit 307 adjusts an ejection intervalbetween the nozzles regarding the row of nozzles that exhibitsdisturbance in sensitivity. Here, as with the first embodiment, timethat is longer than time with which it is possible to settle the stirredliquid droplets so that the majority of the liquid droplets ejected inthe preliminary ejection can reach the waste ink absorber 405 is set asthe wait time (defined as t3; see FIGS. 10A and 10B). This settingenables ejection of the next nozzle in the state where the effect of thestir of the liquid droplets generated by ejection are settled.Accordingly, it is possible to accurately determine whether or not thenozzle is in the state of ejection failure in the course of thedetection of the state of ejection carried out in S1106 and so on.

In S1109, the sequence control unit 307 detects the state of ejection ofthe nozzle by using the liquid droplet detection sensor 205. To be moreprecise, the light receiving element 402 can obtain a signal indicatingwhether or not the ink droplet ejected from the nozzle in S703 passesacross the light flux 404 by means of reception of the light. Thedetection processing in this step is executed one by one for all thenozzles provided to the print head 201. As a consequence of adjustmentof the ejection interval between the nozzles in S1105, the ejectioninterval between the nozzles to be applied to the nozzle determined tohave the stir in this step is longer than the ejection interval to beapplied to the nozzle determined not to have the stir.

Effect of Present Embodiment

According to the present embodiment, all the nozzles targeted forinspection are subjected to the determination of presence of the stir ofthe liquid droplets before determining whether the nozzles are in thestate of normal ejection or in the state of ejection failure. In thisway, it is possible to improve accuracy of determination as to whetheror not the nozzle is in the state of normal ejection or in the state ofejection failure.

Other Embodiments

Embodiment(s) of the present disclosure can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

According to the present disclosure, it is possible to maintain accuracyin detecting a state of ejection of liquid droplets from a nozzle so asto prevent erroneous detection while suppressing an increase indetection period.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2022-092338, filed Jun. 7, 2022, which is hereby incorporated byreference wherein in its entirety.

What is claimed is:
 1. A printing apparatus comprising: a print headincluding a plurality of nozzles each configured to eject a liquiddroplet to a print medium; a control unit configured to control drive ofeach of the nozzles so as to eject the liquid droplet; a sensorconfigured to detect the liquid droplet ejected from each of thenozzles; a determination unit configured to perform determination as towhether or not stir of the liquid droplet is present in a case whereeach of the nozzles is driven by the control unit; and an adjustmentunit configured to perform adjustment of an ejection interval betweenthe nozzles in a case of detecting the liquid droplet by using thesensor, the adjustment being carried out based on the determination asto whether or not the stir is present.
 2. The printing apparatusaccording to claim 1, further comprising: an assumed ejection failuredetermination unit configured to determine one target nozzle out of theplurality of nozzles driven by the control unit as the target nozzlehaving an assumed ejection failure in a case where the sensor fails todetect the liquid droplet from the target nozzle; and a designation unitconfigured to designate a nozzle group including the nozzle determinedto have the assumed ejection failure by the assumed ejection failuredetermination unit, wherein the determination unit determines whether ornot the stir is present by causing the control unit to drive each of thenozzles in the nozzle group, and each of the nozzles determined to havethe stir is subjected to detection of the liquid droplet again by usingthe sensor.
 3. The printing apparatus according to claim 2, furthercomprising: a carriage configured to reciprocate the print head in amain scanning direction, wherein the determination unit generates agraph showing a relation between a position of the carriage and numberof the nozzles by plotting a counted value of the number of nozzles,from which the sensor detects the liquid droplet in a case where thecontrol unit drives each of the nozzles in an inspection area set toinclude the nozzle group, and the determination as to whether or not thestir is present is carried out by comparing the generated graph with areference graph.
 4. The printing apparatus according to claim 1, whereinthe control unit is enabled to eject the liquid droplet from each of thenozzles at desired timing by using an ejection signal.
 5. The printingapparatus according to claim 1, wherein the sensor includes a lightemitting element, and a light receiving element configured to receive alight flux emitted from the light emitting element, and the liquiddroplet ejected from the print head blocks the light flux.
 6. Theprinting apparatus according to claim 1, wherein the print head includesa row of nozzles including the plurality of nozzles arranged in apredetermined direction, and the print head includes a plurality of therows of nozzles.
 7. The printing apparatus according to claim 6, furthercomprising: a transportation unit configured to transport the printmedium in a direction of transportation, wherein the predetermineddirection is the direction of transportation.
 8. The printing apparatusaccording to claim 3, wherein the direction of transportation is adirection orthogonal to a main scanning direction.
 9. The printingapparatus according to claim 2, wherein the nozzle group includes afirst nozzle determined to have an assumed ejection failure by theassumed ejection failure determination unit, and a second nozzle in therow of nozzles to which the first nozzle belongs.
 10. The printingapparatus according to claim 2, wherein the nozzle group includesnozzles located at anteroposterior positions adjacently to a nozzledetermined to have an assumed ejection failure by the assumed ejectionfailure determination unit.
 11. The printing apparatus according toclaim 1, wherein the determination unit performs the determination as towhether or not the stir is present regarding all of the nozzles includedin the print head.
 12. The printing apparatus according to claim 11,wherein the ejection interval to be set to the nozzle determined to havethe stir is longer than the ejection interval to be set to the nozzledetermined not to have the stir.
 13. A method of controlling a printingapparatus including a print head including a plurality of nozzles eachconfigured to eject a liquid droplet to a print medium, a control unitconfigured to control drive of each of the nozzles so as to eject theliquid droplet, and a sensor configured to detect the liquid dropletejected from each of the nozzles, the method comprising the steps of:performing determination as to whether or not stir of the liquid dropletis present in a case where each of the nozzles is driven by the controlunit; and performing adjustment of an ejection interval between thenozzles in a case of detecting the liquid droplet by using the sensor,the adjustment being carried out based on the determination as towhether or not the stir is present.
 14. The method according to claim13, further comprising the steps of: determining one target nozzle outof the plurality of nozzles driven by the control unit as the targetnozzle having an assumed ejection failure in a case where the sensorfails to detect the liquid droplet from the target nozzle; anddesignating a nozzle group including the nozzle determined to have theassumed ejection failure in the determining, wherein the determiningincludes determining whether or not the stir is present by causing thecontrol unit to drive each of the nozzles in the nozzle group, and eachof the nozzles determined to have the stir is subjected to detection ofthe liquid droplet again by using the sensor.
 15. A non-transitorycomputer readable storage medium storing a program to cause a computerto execute a method of controlling a printing apparatus including aprint head including a plurality of nozzles each configured to eject aliquid droplet to a print medium, a control unit configured to controldrive of each of the nozzles so as to eject the liquid droplet, and asensor configured to detect the liquid droplet ejected from each of thenozzles, the method comprising the steps of: performing determination asto whether or not stir of the liquid droplet is present in a case whereeach of the nozzles is driven by the control unit; and performingadjustment of an ejection interval between the nozzles in a case ofdetecting the liquid droplet by using the sensor, the adjustment beingcarried out based on the determination as to whether or not the stir ispresent.